33 kV system with NER

[Power0020]

During faults, the 33 kV sound phases will be subjected to voltages about 1.73 pu, how this is going to impact the equipment other than Surge arrestors? I understand that cables will tolerate the overvoltage for short time given it is not exceeding 125 hours a year. What about trasformers?

 

[Parchie]

I'll take a wild shot here.

Maybe you meant a line to ground fault? The line that makes contact will be at ground potential while the other two gets elevated voltages, depending on how your system is installed. That said, any weak point/s in your system will get damaged as your system capacitance gets charged (will usually experience higher voltage if your system is not effectively grounded). I haven't seen transformers failing ahead of other elements though.

 

[jghrist]

Is any of the equipment rated for line-to-ground voltage?

 

[Mbrooke]

You will need phase to phase rated cables, cutouts, insulators and any PTs connected line to ground need to be full phase voltage rated. In a nut shell you will need to design this system as though its a 56kv grounded wye system.





This might be going off subject, but if the neutral resistor impedance is higher than your phase to ground capacitive reluctance arcing ground faults may cause values above 1.73 pu. Of course, on of the reasons for a neutral earthing resistor is to let enough current flow through to mitigate issues with arcing line to ground faults.